Reciprocating gas engines, which are operated with combustion gases having a high energy content, can be operated either according to the Otto method or also according to the so-called diesel-gas method. In both cases, a mixture of air and combustion gas is sucked in and compressed. With the Otto method, ignition occurs through spark-over between the electrodes of a spark plug. With the diesel gas method, ignition occurs via a so-called pilot injection, meaning a metered amount of a self-igniting, liquid ignition fuel, as a rule diesel fuel, is injected with high pressure into the compressed combustion gas-air-mixture to initiate the combustion. This injected ignition fuel self-ignites and thus forms a multitude of spatially distributed ignition sources. The energy released as a result of the injected ignition fuel is considerably higher than the spark energy from a spark plug. This method has advantages with respect to the maintenance costs and the idle times since the spark plugs are subjected to high wear owing to the increase in ignition energy, which decreases the service life drastically.
With a gas engine operating according to the Otto method, full use is made of the special advantage of a considerably lower pollutant emission, particularly of nitrogen oxides, as compared to the gasoline engines or the diesel engines. With a gas engine operating according to the diesel method, the pollutant emission is increased, relative to the "pure" gas engine operating according to the Otto method, because of the fuel injected for the ignition. Until now, the diesel gas method could therefore be used only for very large stationary gas engines with a volume of 20,000 cm.sup.3 and more per cylinder. This is due to the fact that the additional discharge of pollutants caused by the ignition fuel could only be kept low for large engines of this type, relative to the total pollutant discharge of the gas engine. The problem results from the injection process being controlled by the rotational movement of a camshaft and a specified cam profile, so that start and end of the injection and thus also the amount injected with a specified injection fuel admission pressure are not influenced, even though they depend on the speed.
German Patent A-44 19 429 discloses a method for operating a self-igniting, mixture-compressing gas engine, which uses an ignition gas in place of a liquid ignition fuel. It is advantageous to use as ignition gas the same combustion gas that is also used to operate the gas engine in the form of a combustion gas-air-mixture. With the known method a small antechamber is assigned to each cylinder that forms the main combustion chamber. The ignition gas is injected into the antechamber with a pressure that is higher than the compression pressure in the main combustion chamber. The advantage of this method is that only one type of combustion fuel is required, so that a reduction of the emission values can be achieved, particularly for nitrogen oxides. The disadvantage of this method is that it requires an involved engine design resulting from the use of antechambers.